He didn't say manufacturing output but jobs, a more relevant number for that argument would be total labor cost in the sector and it's change over time between two countries.
That's not such a relevant number because plenty of those US jobs went to automation, not to China. There are still over 12 million manufacturing jobs in the US. About 8% of all US jobs which is a significant chunk. Easily disapproving the wild exaggeration that "all of the manufacturing jobs are in China... ".
